Photographic elements having protective overcoat layers are well known and a wide variety of different coating compositions have been proposed in the past for use as protective overcoats. Such overcoats serve a number of different purposes, such as to provide protection against fingerprints, abrasion and scratching, to protect against water spotting, to provide a particular surface texture such as a matte surface, to provide protection against blocking, and to act as anti-reflection layers which reduce glare. Layers of a temporary nature which are intended to be removed after they have served their purpose and layers which are permanently bonded to the photographic element have been described in the prior art. Protective overcoats can be applied to photographic elements by coating solutions or dispersions of film-forming agents in organic solvents such as are described, for example, in U.S. Pat. Nos. 2,259,009; 2,331,746; 2,706,686; 3,113,867; 3,190,197 and 3,415,670; by coating of aqueous film-forming compositions such as are described, for example, in U.S. Pat. Nos. 2,173,480; 2,798,004; 3,502,501 and 3,733,293; by coating of compositions containing discrete, transparent, solid particles of submicroscopic size as described in U.S. Pat. No. 2,536,764; by coating of plasticized polymer compositions as described in U.S. Pat. No. 3,443,946; by coating of polymerized perfluorinated olefins as described in U.S. Pat. No. 3,617,354; and by lamination of a protective layer as described, for example, in U.S. Pat. Nos. 3,397,980 and 3,697,277.
Many of the compositions used in the past to form protective overcoats on photographic elements have suffered from disadvantages which have greatly limited their usefulness. For example, it has been particularly difficult to formulate compositions which are fully satisfactory in providing abrasion and scratch resistance for photographic elements which are commonly subjected to severe conditions in handling and use, such as microfiche and motion picture films. Abrasion is particularly a problem because in all stages of preparation, use and development the film contacts other objects such as rollers and the like. For example, in motion picture film the film contacts various elements in the projection apparatus capable of abrading the film as a result of the contact. Protective overcoats for photographic elements must furthermore meet exacting requirements with respect to factors such as transparency and flexibility as well as abrasion resistance and scratch resistance, and must be very strongly bonded to the underlying material to avoid the possibility of delamination. Protective overcoats for photographic elements must also contain a sufficiently high percentage of solids to provide the desired protective characteristics but also have a sufficiently low viscosity to be coatable by machine methods such as roll coating.
While the coating compositions of the aforesaid patents represent an advance in the art of providing protective overcoats for photographic elements, still further improvement in such compositions would be highly desirable. It would be particularly advantageous to provide a coating composition which exhibits excellent adhesion toward processed photographic emulsion layers and toward all of the various types of support materials commonly used for photographic elements, for example, the cellulose acetate support materials and the polyester support materials. A problem can occur, however, in providing a coating composition capable of overcoating a surface with sufficient coverage of solids to provide the desired abrasion and scratch resistance while having a viscosity low enough to be coatable by various machines and processes. It would be particularly advantageous for the coating composition to be applicable to the element by a number of means, for example, by dip coating, roll coating, gravure coating, and the like.